The lighting control system uses a combination of computer, communication and digital dimming technology to automate the lighting system according to the function, time period, indoor brightness or the use of the area. With the rapid development of the building automation and lighting industry, lighting control systems with energy-saving design and digital control as the core will be an inevitable trend in the development of the lighting market.
DALI (Digital Addressable Lighting Interface) is an internationally-recognized lighting control communication protocol with a communication speed of 1200 BPS±10%, and mainly used for dimming control of multiple fluorescent lamps and LED lighting. DALI can form a network by a maximum of 64 short addresses and 16 group addresses, and one host can control one or more slaves to communicate in half-duplex mode.
The DALI interface communication protocol has simple coding and reliable communication. Its main electrical characteristics are as follows: 1. asynchronous serial communication, information transmission rate is 1200 baud/s; 2. half-duplex, two-line differential drive, data transmission using Manchester coding mode; 3. The voltage difference of the DALI bus is used to judge the level. The voltage difference is 1 between 9.5 and 22.5V, 0 between −6.5 and 6.5V; 4. DALI bus current is less than 250 mA; 5. The rise and fall time of DALI signal is 10˜100 μs.
The level of the DALI bus is different from the level of the microcontroller. In order to complete the communication between the host and the slave, an interface circuit must be provided to implement level shifting between the DALI bus and the microcontroller. The interface circuit is a difficult point in the design of the DALI system, mainly because it must meet the electrical characteristics of the DALI protocol.
The DALI interface circuit includes a host interface circuit and a slave interface circuit. The present application is directed to a slave interface circuit. In the prior art, in the communication process of the DALI bus, the DALI bus needs to be short-circuited, and pull the bus voltage down from high to low level. The N-channel MOS transistor is usually used for short-circuit operation during operation. The turn-on voltage of the N-channel MOS transistor is between 2 and 4V, but since the power supply voltage of the microcontroller is usually 3.3V, it cannot effectively ensure that the MOS transistor is turned on. Therefore, in the existing product design, the power supply part needs to design a power supply of 5V or more to supply power to the driving circuit of the MOS tube to turn on the MOS tube. However, the design of the power supply circuit causes the entire circuit to become complicated, the cost rises, and the stability is degraded.